@chandraskhar
May I double-check the Model number and hardware version of your Range Extender?
If the Wi-Fi led or signal goes off, and only power is ON, you could try factory reset the extender and set it up with router again using Tether app or web UI.
RESET: with RE powered on, use a pin to push the reset hole until all the Leds flash once.
Follow instructions on Tether app or Web page step by step ( carefully examine the Wi-Fi password you have put in, and it is recommended to create a different SSID/WiFi name for RE )
How to log into the web management page of the range extender (new logo)?
https://www.tp-link.com/us/support/faq/1398/